(This article is an original article from Bisheng. It is forbidden to reprint, and reprinting must be corrected) Lamination is an important printing process in post-press processing. Although the process is not very complicated, in the operation and process design of lamination, it often occurs because of a lack of sufficient understanding of the lamination itself and printing. Or that kind of problem. In this article, we will analyze some of the problems often encountered in laminating and propose some solutions. Laminating is a comprehensive technology, which involves many factors, such as plastic films, adhesives, solvents, ink layer conditions on printed products, mechanical control, and environmental conditions. In order to obtain high-quality coated products, it is necessary to control the changes of the above factors and coordinate the relationship between them during the process. Second, the processing technology The process flow of coating is: process preparation → installation of plastic film roller → application of adhesive → drying → setting of process parameters (drying tunnel temperature and hot pressing temperature, pressure, speed) → trial coating → sampling inspection → formal Laminating → rewinding or splitting. 1. Process preparation work. Whether the preparation work is sufficient has a great influence on ensuring the normal production of film production, improving production efficiency and product quality. The preparation of film production should generally include: inspection of the printed matter to be coated, selection of plastic film and preparation of adhesives. (1) Inspection of printed matter to be answered. The inspection of laminated printed materials is different from the quality inspection of ordinary printed materials. Mainly should be directed to the items with greater influence of the coating, such as whether there is powder spray on the surface, whether the ink is sufficiently dry, and whether the printed matter is smooth, etc. Once the problem is found, it should be taken in time. (2) Selection of plastic film. The selection of plastic film includes the selection of plastic film, quality inspection and slitting roll material. Whether the coating material is appropriate is an important factor related to product quality. Commonly used plastic films are: polyvinyl chloride (PVC), polypropylene (BOPP) and polyester (PET) films. Among them, BOPP film (15 ～ 20μm) is flexible, non-toxic, and has good flatness, high transparency, good brightness, and has the properties of wear resistance, water resistance, heat resistance, chemical resistance, etc. In addition, its price is cheap, it is covered The ideal composite material in membrane technology. The quality requirements of the plastic film on the film coating process are: the thickness directly affects the light transmittance, refractive index, film fastness and mechanical strength of the film. According to the performance of the film itself and the purpose of use, the thickness of the film is 0.01 ~ 0.02mm Between is appropriate. It must be treated by corona or other methods. The surface tension of the treated surface should reach 4Pa in order to have better wettability and adhesion performance. The corona treated surface should be uniform. The higher the transparency, the better, in order to ensure that the printed matter covered has the best clarity. Transparency is expressed in terms of light transmittance, which is the percentage of transmitted light and projected light; the light transmittance of PET film is generally 88 to 90%, and the light transmittance of other films is usually 92 to 93%. Good light resistance, that is, it is not easy to change color when exposed to light for a long time, and has certain mechanical strength and flexibility characteristics. The mechanical strength of the film includes tensile strength, elongation at break, elastic modulus, impact strength, and folding resistance. index. The geometric dimensions should be stable, which are usually expressed by indicators such as the coefficient of hygroscopic expansion, the coefficient of thermal expansion, and the temperature of thermal deformation. The film-covered film must have certain chemical stability in contact with solvents, adhesives, inks, etc. The appearance of the film surface should be smooth, without unevenness and wrinkles, and the film should be free of bubbles, shrinkage holes, pinholes and pits, etc., and the film surface should be free of dust, impurities, grease and other pollution. Uniform thickness, small vertical and horizontal thickness deviation; due to the limited adjustment ability of the laminating machine, rewinding is also required, and the ends are uniformly tight to ensure uniform glue application. Of course, the cost is lower. Except for the above-mentioned surface treatment of the film surface, most of the quality inspection methods of plastic films can be solved by hand or visual inspection. Wide-roll film rolls must also be cut into narrow-roll rolls according to the required width before they can be used for laminating. The narrow-roll rolls after slitting must have flat edges, flat ends and uniform curling tension. (3) Preparation of adhesive. There are many types of adhesives used in China, mainly polyurethanes, rubbers and thermoplastic polymer resins. Among them, the use of thermoplastic polymer adhesives is the best. Solvent-based adhesives are widely used. Commonly used solvents include vinegars (such as ethyl acetate), alcohols, and benzenes (such as toluene). Solvent-based adhesives are divided into one-component and two-component. The one-component adhesive is easy to use and has a low cost. Although the bonding strength is slightly lower than that of the two-component adhesive, other technical measures can be used to make up for it, and it is more commonly used. Although the two-component adhesive has high bonding strength, it is expensive and cumbersome to use. Various adhesives should meet the following requirements: light color, high transparency; no precipitated impurities; good dispersion performance, easy flow, good dryness; non-toxic or low-toxic solvents; good long-term adhesion performance, good for ink and paper 〠Plastic film has good adhesion; long-term placement of film-covered products will not yellow, wrinkle, foam or delamination; and require adhesives with high temperature resistance, low temperature resistance, acid and alkali resistance and easy operation , Cheap and other features. The one-component adhesive can be used directly. Two-component or multi-component adhesives will react as soon as they are mixed, and the adhesive strength of the adhesive will decrease as the storage time increases due to surface aging. Therefore, the formulated adhesive should not be stored for a long time. , It should run out in days. The quality of the coating has a great relationship with the quality of the preparation of the adhesive, and care should be taken when preparing. 2. Install the plastic film reel. After cutting the selected film to the appropriate width according to the width of the printed matter, it is installed on the unwinding device of the laminating machine, and the plastic film is passed through the coating mechanism. It is required that the film is smooth and wrinkle-free, and the tension is uniform and moderate. If the printed film is to be made into a carton, it must be considered to leave a gap in the interface, otherwise the bonding will not be strong. 3. Apply adhesive. First of all, the viscosity of the adhesive should be determined by factors such as the quality of the paper, the thickness of the ink layer, the temperature of the drying tunnel, the length of the drying tunnel, and the speed of rotation of the machine. When the ink layer is thick, the drying tunnel temperature is low, the drying tunnel is short, and the machine speed is fast, the viscosity of the adhesive should be appropriately increased, and vice versa. Secondly, the thickness of the coated adhesive layer should be mastered to make it uniform. The thickness of the coating depends on the quality of the paper and the thickness of the ink layer: coated paper with a smooth surface, the coating amount is generally 3 to 5g / m (about 5μm thick); offset paper and white board with rough surface and large ink absorption Paper, the coating amount is 7-8g / m (about 8μm thick). Of course, the ink layer is thick and the coating amount should be slightly larger, and vice versa. However, if the coating is too thick, it is easy to foam and wrinkle, otherwise the coating is not strong. 4. Drying. The purpose is to remove the solvent in the adhesive and retain the solid content of the adhesive. The temperature of the drying tunnel should be controlled between 40 ～ 60 ℃, mainly determined by the volatility of the solvent in the plastic adhesive. The dryness of the adhesive layer is generally controlled at 90-95%. At this time, the adhesive force is large and the paper-plastic composite is the strongest. If the coating is uneven or too dry, it will reduce the adhesion and cause blistering and delamination of the coating. 5. Adjust the hot pressing temperature and the pressure between the rollers. The hot pressing temperature is adjusted according to the thickness of the ink layer of the printed matter, the quality of the paper, the climate change, etc., and should generally be controlled at 60 to 80 ° C. If the temperature is too high, it will exceed the bearing range of the film. The film will be deformed by high heat, which is easy to curl, foam, wrinkle, etc., and the surface of the rubber roller is easy to be scalded and deformed. Floor. Generally, the hot-pressing temperature of coated paper is lower, and the hot-pressing temperature of offset paper, whiteboard paper, and thick-printed ink is higher. The pressure between the rollers should be adjusted according to different paper quality and paper thickness. When the pressure is too large, the paper surface is slightly uneven or the film tension is not completely consistent, it will produce wrinkles or streaks; too long pressure will cause the rubber roller to deform, and the roller bearings will also wear due to excessive force . If the pressure is too high or uneven, it will cause the film to be weak and delamination. Generally, the printed products with smooth, flat and strong coating surface have a pressure of 19-20mPa; the printed products with rough coating are 22-22mPa. 6. Speed ​​control. The faster the machine speed, the shorter the hot pressing time, so the temperature can be adjusted higher, the pressure can be increased, and the viscosity of the adhesive should be greater; and vice versa. The machine speed is generally controlled at 6 ～ 10m / min. If the machine speed is too fast or too slow, the film quality will be affected. 7. Sample testing. Samples are drawn after the film is tested, and key performance tests are performed on the sampled products in accordance with product standards. It is required to achieve a bright and smooth surface, without wrinkles, bubbles, and delamination. 8. Stereotype segmentation. If the coated product is printed on white paper, it should be divided immediately, and the film side should be placed up; the thinner coated paper and offset paper printed should be rewinded and placed for 24h before it can be divided, which can improve the adhesion. , And can prevent a single sheet of paper from curling. Third, the impact of printing processing on the film The effect of lamination is not only related to the raw material of the film and the operation method of the film, but more importantly, it is also related to the condition of the ink layer of the printed matter being stuck. The condition of the ink layer of the printed matter is mainly determined by the nature of the paper, the performance of the ink, the thickness of the ink layer, the area of ​​the graphic and the integral density of the printed graphic, etc. These factors affect the forming conditions of the bonding mechanical bonding, physical and chemical bonding, etc. Changes in surface adhesion properties. 1. Thickness of ink layer of printed matter. Solid prints with thick ink layers are often difficult to adhere to plastic films and will soon delaminate and foam. This is because the thick ink layer changes the porous surface characteristics of the paper and closes the paper fiber capillary pores, which seriously hinders the penetration and diffusion of the adhesive. The penetration of the adhesive within a certain degree is beneficial to the adhesion of the film. In addition, if the ink layer and the ink layer area on the surface of the printed matter are different, the adhesion and wetting properties are also different. The experiment proves that with the increase of the thickness of the ink layer or the increase of the graphic area, the surface tension value decreases significantly. Therefore, whether it is monochrome printing or multi-color printing, we should strive to control the thickness of the ink layer to be thin. The thickness of the printing ink layer is also directly related to the printing method. The printing method has different thicknesses. For example, the thickness of the ink layer of a lithographic product is about 1 to 2 μm, about 2 to 5 μm during relief printing, and up to 10 μm during gravure printing. From the perspective of lamination, offset printing is ideal, and its ink layer is very thin. 2. The type of printing ink. The printed matter that needs to be covered with film should use fast-fixing bright offset printing ink. The connecting material of the ink is composed of synthetic resin, dry vegetable oil, high boiling point kerosene and a small amount of colloid. Synthetic resin molecules contain polar groups, which are easy to diffuse and penetrate with the polar groups in the binder molecules, and produce cross-linking, forming physical and chemical binding force, which is conducive to coating; fast fixation The bright offset printing ink also has the advantage of quickly drying the conjunctiva after printing, which is also very beneficial for laminating. However, it is not advisable to add too much drier during use, otherwise, the surface of the ink layer will be crystallized, which will affect the coating effect. 3. Use of ink diluent. Ink diluent is a kind of substance that can lighten the color of ink. Commonly used ink diluents include white ink, Willy oil, and bright oil. White ink belongs to the category of inks and consists of white ink pigments, linking materials and auxiliary materials. It is often used for light solid printing, spot color printing and trademark pattern printing. Inferior white ink has obvious powdery particles and is not tightly bound to the binder. After printing, the binder will quickly penetrate into the paper, and the pigment will float on the paper to form an obstacle to adhesion. This is that some light-colored solid prints are often not easy to be coated. s reason. Choose white ink carefully before printing, try to use even and fine white ink without obvious particles as the diluent. Veli oil is a paste-like transparent body made of aluminum hydroxide and dry vegetable oil connecting material dispersedly rolled, which can be used to increase the gloss of the surface of the printed matter and has excellent printing performance. However, aluminum hydroxide is light in weight and will float on the surface of the ink layer after printing. When coating, the adhesive layer and the ink layer will form an imperceptible separation layer, resulting in poor adhesion or blistering. It is slow to dry itself, and also has the characteristics of inhibiting ink drying, which is also difficult to adapt to the coating. Gloss oil is a kind of quick-drying diluent from inside to outside. It is a colloidal transparent substance made by mixing resin, dry vegetable oil, drier and so on. The texture is delicate: the conjunctiva is bright and has good affinity. ， Polypropylene film can be firmly adsorbed on the surface of the ink layer. At the same time, the varnish can make the blots shiny and dry faster, and the printing performance is good. Therefore, it is an ideal ink diluent. 4. Add powder. In order to adapt to multi-color high-speed printing, powder spraying process is often used in offset printing to solve the disadvantage of dirty back. Powder spraying is mostly composed of cereal starch and natural suspended substances. The anti-sticking effect of powder spraying is mainly to form an irreversible cushion on the surface of the ink layer, thereby reducing adhesion. Because the particles are coarse, if too much powder is sprayed during the printing process, these particles float on the surface of the printed product. The adhesive does not adhere to the ink layer everywhere during the film coating, but to this layer of powder spray, resulting in false Sticking phenomenon seriously affects the quality of the coating. Therefore, if the post-printed products need to be coated, the amount of powder sprayed should be controlled as much as possible during printing. 5. The dry condition of the ink layer on the surface of the printed matter. The poor drying of the ink layer of the printed matter is extremely harmful to the quality of the film. In addition to the factors that affect the drying of the ink layer, in addition to the type of ink, the amount and type of drier in the printing process, and the ambient temperature and humidity of the printing and storage room, the structure of the paper itself is also very important. If the structure of coated paper and offset paper are different, the drying condition of the ink layer is also different. Regardless of whether it is coated paper or offset paper, covering the film when the ink is not completely dried completely has an adverse effect on the quality of the coating. The high boiling point solvent contained in the ink is easy to expand and stretch the plastic film, and the expansion and elongation of the plastic film are the most important reasons for the foaming and delamination of the product after coating. Four, common faults and solutions There are many factors that affect the quality of the film. In addition to objective factors such as paper, ink layer, film, adhesive, etc., it is also affected by subjective factors such as temperature, pressure speed, and amount of glue. If these factors are not handled properly, various coating quality problems will arise. 1. Poor adhesion. A. If the adhesive is selected improperly, the amount of glue is not set properly, and the ratio measurement is incorrect, the failure of the film adhesive bond should be reselected. B. If the surface condition of the printed matter is poor, such as powder spraying, the ink layer is too thick, the ink is not dry or not completely dry, etc., causing poor adhesion, you can use a dry cloth to gently wipe off the powder, or increase the adhesive coating The amount, increase the pressure, and apply hot pressing again before gluing, or change to a high solid content adhesive, or increase the thickness of the adhesive coating, or increase the drying channel temperature and other solutions; C. If the adhesive is absorbed by the printing ink and paper, and the coating amount is insufficient, consider resetting the formula and coating amount. D. Check whether the film corona treatment reaches 36-40 dynes. E. Inadequate bonding at the edge. This is mainly reflected in thick paper. The paper will curl to a certain degree during winding. And the smaller the winding diameter is, the more obvious it is. The coated product that has just been dried out from the pressure roller is often pushed up by the curled paper at the overlapping edge, resulting in poor adhesion here. In order to improve the yield, the width of the overlap should be reduced as much as possible to ensure that the width of the bonding is not within the range of the die cutting bite. 2. Foaming. A. If the reason is that the printing ink layer is not dry, it should be hot pressed and glued again. You can also postpone the coating date and let it dry completely; B. The pressure of the pressure roller is too small There are bubbles on the entire surface of the printed matter because the pressure is too small, and the pressure of the pressure roller can be increased appropriately. B. If the printing ink layer is too thick, you can appropriately increase the amount of adhesive coating, increase the pressure and compound temperature; C. If the surface temperature of the composite roller is too high, heat dissipation measures such as air cooling and closing the heating wire should be taken to reduce the temperature of the composite roller as soon as possible; D. If the drying temperature of the film is too high, it will cause skinning on the surface of the adhesive and foaming failure will occur. At this time, the drying temperature should be appropriately reduced; E. The blistering failure caused by the film being wrinkled or slack, uneven or curled, can be solved by adjusting the tension or replacing the qualified film; F. One of the reasons is the high concentration of adhesive, high viscosity, uneven coating, and low dosage. At this time, thinner should be used to reduce the concentration of adhesive, or to appropriately increase the amount and uniformity of coating. G. There are air bubbles at the overlap of the two papers because the front and back papers are stuck together when laminating. This is mainly reflected in thick paper. If the print bite is large, you can adjust the equipment to make the two papers have a certain amount of overlap; when the bite is small, the two papers can be properly pulled apart, but the tail film will appear after slitting. Therefore, the distance should not be too large. H. The storage of printed matter is generally stacked on thousands of sheets. This causes the paper to not absorb moisture evenly across the entire area, and the edge area should be faster, which is the reason for the ruffles. Prints with ruffles will flatten out under laminating pressure, and will return to their original state after exiting the pressure roller. This creates bubbles. The solution is to humidify or loosen the print on the lotus leaf to dry. 3. Uneven coating. A. Uneven thickness of the plastic film, too small compound pressure, loose film, curing of part of the adhesive in the rubber tank, swelling or deformation of the rubber roller will cause uneven coating; B. After the fault occurs, the cause should be found as soon as possible and corresponding measures should be taken, either to adjust the traction force, increase the composite pressure, or replace the film, rubber roller or adhesive. 4. Wrinkled film. The reasons are generally unbalanced film conveying rollers, inconsistent tightness or wavy edges at both ends of the film, excessive thickness of the rubber layer, or uneven ends of the heating roller and rubber roller, inconsistent pressure, and different linear speeds. Roll to equilibrium, replace the film, adjust the amount of glue and increase the temperature of the drying tunnel, adjust the position and process parameters of the electric heating roller and rubber roller. 5. Laminated products are warped. A. The reason is that the printed matter is too thin, the tension is unbalanced, the film is pulled too tight, the compound pressure is too high, or the temperature is too high, etc .; B. The corresponding treatment method is to avoid laminating the thin paper as much as possible; C. Adjust the tension of the film to make it reach balance; appropriately reduce the compound pressure and reduce the compound temperature. 6. The product has snowflake points. A. If the print powder is too large, it cannot be completely dissolved by the glue, and there will not be a large area of ​​snowflakes. In this case, the amount of glue should be increased or the print powder should be cleaned before laminating. B. If the amount of glue is too small, snowflakes will appear on the entire surface of the printed matter. The solution is to appropriately increase the amount of glue. C. If the pressure of the pressure roller is too high, the glue at the edge of the printed matter will be squeezed out, resulting in snowflakes at the edges of the printed matter; otherwise, the pressure will also appear. The solution is to adjust the pressure of the pressure roller. D. There is a small amount of glue in the area where the glue roller has dry rubber, which will cause snowflakes on the coated product. The solution is to wipe the glue roller clean. E. The glue extruded from the edge of the printed product or the glue extruded from the pinhole of the film sticks to the pressure roller. After a long time, a dry rubber ring will be formed, and tiny snowflakes will appear here when the subsequent printed product is covered with film. The solution is to wipe the pressure roller in time. F. If there is too much dust in the surrounding environment or there is dry rubber and cut film fragments in the glue, the coated product will have snowflakes, so you should pay attention to the environmental hygiene, the glue can't be used up, you should return it to the glue bucket to seal it, Or take the method of filtering before gluing. 7. The product curls after slitting. A. Excessive tension of the film will cause it to elongate and deform. After the product is cut, the external force will be removed, and the film will return to its original shape, causing the product to curl to the side of the film. The solution is to adjust the screwing depth of the film tightening screw to reduce the braking force. . B. Too much winding tension will cause the film and printed matter to deform simultaneously, but the amount of deformation is different. After the external force is removed, the product will curl to the side of the paper, especially the thin paper. The solution is to reduce the friction force of the winding power wheel (friction sprocket). C. After the coated product is fully dried, the paper will be dehumidified and deformed, and the finished product will curl to the side of the paper. The solution is to control the humidity in the workshop. D. Short drying time 8. The product becomes black. This is mainly manifested in large-area printing and bronzing products. This is due to the chemical reaction between the chemically active elements in the glue and the gold powder. The solution is to use special gold ink or special glue for the gold printing products, or the gold foil products to be coated first and then gold foil. Wearable Breast Pump,Electric Wearable Breast Pump,Breast Pump Hands Free,Wireless Breast Pump Zhejiang Carebao Co., Ltd , https://www.carebao.com